A spokesman for the Deterrence Force, which acts as Government of National Accord's police, said the brother was aware of Abedi's plan and the two brothers were both members of the Islamic State group.

The attack was claimed by IS jihadists.

Hashem had been "under surveillance for a month and a half" and "investigation teams supplied intelligence that he was planning a terrorist attack in the capital Tripoli", the Deterrence Force said on its Facebook page.

A relative told AFP that Abedi had travelled to Manchester from Libya four days before the bombing.

"It's very clear that this is a network that we are investigating," Manchester police chief Ian Hopkins told reporters, with five people now under arrest.

The British government announced a nationwide minute's silence for 11:00am (1000 GMT) Thursday in memory of those killed and the dozens wounded.

Manchester police arrest suspect in Wigan

0:00

00:00 / 00:00

Share

'Act of cowardice'

The attack was the latest in a series of deadly incidents across Europe claimed by IS that have coincided with an offensive on the group's redoubts in Syria and Iraq carried out by US, British and other Western forces.

Officials said Abedi, 22, had been on the radar of the intelligence community before the massacre and warned another attack "may be imminent".

After arresting a 23-year-old man on Tuesday, police said they had taken three more men into custody on Wednesday in south Manchester, where Abedi lived.

A fifth man who was carrying a suspect package was then detained in Wigan, northwest of the city.